swarms of small black flying insects

About a week ago we noticed swarms of these little black bugs. We live not far from the wetlands and are new to the area. At first we thought they were mosquitos. Then we wondered if the were gnats. ( what is a gnat anyway?!) They have sourounded our house. The are black, have two wings and six legs. The look similiar to mosquitos. Does anyone know what they are and what we can do about them?